1. Field of the invention
The present invention relates to an image recording apparatus such as a copying machine or a printer in which a recording medium is employed and more particularly to a pressure developing device which applies pressure to the recording medium.
2. Description of the Related Art
Generally, an image recording apparatus of this kind employs, for instance, as disclosed in U.S. Pat. No. 4,920,375, a continuous form of photosensitive and pressure sensitive recording medium coated with a plurality of photosensitive and pressure sensitive microcapsules with each of said microcapsules enveloping therein a chromogenic material and a photo-curable resin, and a developer medium provided with a developing material which provides an output image upon reaction with the chromogenic material.
The image recording apparatus comprises an exposure unit for exposing an optical image on photosensitive and pressure sensitive recording medium, a pair of pressure developing rollers adapted to be brought into and out of contact with each other, for pressurizing the exposed recording medium to develop a visible image, a drive unit for rotating at least one of the pressure developing rollers, a shift unit for shifting at least one of the pressure developing rollers toward or away from the other one of the pressure developing rollers, and a control unit for controlling said drive unit and said shift unit such that one of the pressure developing rollers is rotated by said drive unit when said one of the pressure developing rollers is shifted.
Further, the image recording apparatus as disclosed in U.S. Pat. No. 4,714,943 comprises a pressure strength adjusting mechanism which is constructed such that one of the rollers is biased toward the other of the rollers by coil springs through a plurality of contact rollers, and the coil springs are arranged so that the pressure strength of the coil spring is distributed corresponding to a gradual decrease from the center portion to both end portions in the direction of the axis of one of the rollers by adjustment of the lengths of the coil springs in a direction of compression.
With the above image recording devices, the latent image is formed on the recording medium by exposing the optical image thereon to selectively cure the photo-curable resins enveloped in the microcapsules existing on the area to which the optical image is exposed. The latent image thus formed on the recording medium is then transferred and developed on the separate developing medium.
Transfer of the image is executed by superposing the recording medium and the developing medium one on the other and pressurizing the superposed mediums by a pair of pressure developing rollers rotated by the drive unit while being kept in contact with each other by the shift unit, so that the softened microcapsules on the recording medium are ruptured by the applied pressure and the chromogenic materials enveloped therein stream out of the ruptured microcapsules. The stream of chromogenic materials react with the developer coated on the developing medium so as to form the visible image thereon corresponding to the above latent image.